Fecal Occult Blood Test

In fecal occult blood test, three separate stool specimens are analyzed for trace amounts of blood that cannot be detected with the naked eye (occult blood). Normally, extremely small quantities of blood are excreted in the feces; by using microscopic and chemical analysis, this test can detect larger amounts that indicate bleeding in the gastrointestinal tract. Doctors currently recommend that all adults over age 50 have an annual fecal occult blood test to screen for colorectal cancer.

Purpose of the Fecal Occult Blood Test

To screen for premalignant growths in the colon or rectum and for colorectal cancer in asymptomatic individuals

To detect blood in the stool in people who are experiencing abdominal pain, diarrhea, vomiting, decreased appetite, or other symptoms

Who Performs Fecal Occult Blood Test

A laboratory technician

Special Concerns about Fecal Occult Blood Test

False-negative results may be caused by taking vitamin C supplements or antacids or by delaying transport of the stool samples for analysis.

False-positive results may result from failure to follow dietary or medication restrictions, or the presence of bleeding gums, hemorrhoids, menstrual blood, or watery stools.

Before the Fecal Occult Blood Test

For seven days before the test, do not take any antacids, iron supplements, steroids or nonsteroidal anti-inflammatory drugs such as aspirin, ibuprofen, or naproxen. (Your doctor may also instruct you to avoid certain other medications).

The following instructions should be carried out for three days before the test to maximize the accuracy of results.

Do not take vitamin C supplements or eat large quantities of foods, such as citrus fruits, that contain this vitamin.

Eat a high-fiber diet, containing whole grains, beans and vegetables that do not contain peroxidase, to increase the bulk of the stools.

Do not drink alcohol and avoid any other substances that may irritate the digestive tract.

If your gums tend to bleed, avoid brushing your teeth.

Women should not begin testing during their menstrual period or during the first three days after the end of their period.

What You Experience during Fecal Occult Blood Test

Your doctor will give you the kit to use for the test.

You will collect stool samples in a clean plastic container for three consecutive days.

Use the wooden applicator supplied with the kit to smear a portion of each sample onto a specimen card.

When you have completed the stool sampling, bring the specimens to your doctor or to a testing laboratory so they can be analyzed for occult blood.

The test takes a few minutes.

Risks and Complications of Fecal Occult Blood Test

There are no risks or complications associated with this test.

After the Fecal Occult Blood Test

After you have completed the stool sampling process, you may resume your normal diet and any medications that were discontinued before the test.

Results of Fecal Occult Blood Test

Your stool samples are analyzed using various methods. They may be examined under a microscope, and may also be treated with special chemicals that can identify hemoglobin, a red blood cell pigment.

If occult blood is detected, your doctor will first attempt to rule out any unrelated factors, such as bleeding gums that might account for this finding.

Because occult blood may result from bleeding at almost any point along the digestive tract, this test is generally used as an initial evaluation in people who show symptoms of gastrointestinal bleeding. Additional tests—such as contrast x-rays or endoscopy of the digestive tract—are required to identify the site and extent of the